Blast-proof water-proof loudspeaker



This invention relates to sound reproducers, and more particularly refers to loudspeakers which are blast-proof, pressure-proof, and water-proof, and which are designed for the intelligible transmission of sound of frequencies within the range of voice communication.

Loudspeakers have many uses which require that their working parts be water-proof. For example, speakers which must be used out-of-doors must be protected against the deteriorating etiects of the weather, particularly where 'the speakers are exposed to rain, ice, snow and salt water atmospheres. Water frequently causes corrosion of the various parts of the speaker, while lower temperatures may cause Water to freeze around the moving parts of a speaker and, particularly in the magnetic gap, to destroy completely the operation of the speaker. iany speakers are used by the military forces where extreme demands are made upon them for performance under adverse weather conditions. For example, loudspeakers are generously distributed throughout naval ships both on deck and below decks. Loudspeakers on deck are exposed tothe elements such as salt water spray and must necessarily be protected. Even more stringent demands are made upon loudspeakers used in the submarine service. Here loudspeakers mounted on the open deck and bridge are completely covered with sea water when the submarine is submerged, and yet they must be immediately ready for operation when the submarine surfaces. They must remain operable even though subjected to 4freezing conditions which would immobilize an ordinary loudspeaker.

Still another requirement for yreproducers used in submarine service and to some extent in other military service is that they be resistant to extreme shocks and pressure changes, such as would be caused by the detonation of depth charges near the submarine. Speakers of known construction have not proved adequate for withstanding such extreme shock.

It is `an object of the present invention to provide a sound reproducer which is not adversely affected by exposure to Water or other potentially harmful agents and which, even when submerged in sea water over an extended period, will remain operable.

I-t is a further object of the present invention to provide a sound reproducer which is extremely resistant to shock land pressure surges, and which will withstand the extreme pressures encountered by submarines while submerging to great depths.

Other objects and advantages of the present invention will become more apparent from the following discussion and from the appended drawings.

According to the present invention, an annular elastomeric centering body having the speaker voice coil substantially embedded therein is disposed in the magnetic gap formed by the pole pieces of the loudspeaker eld magnet. The centering body serves the function of centering the voice coil within the gap and allowing it to vibrate axially, and of providing a biasing force to urge the voice coil to its normal position. It also prevents water and `other corrosive elements as well as dirt from entering the magnetic gap vand impeding the normal operation of the speaker.

ln the drawings:

FIG. 1 is a cross-sectional view, taken through the ...ent

axis and along the line 1-1 of FIG. 2 of a sound reproducer embodying the present invention;

FIG. 2 is a cross-sectional view taken at the line 2 2 of FlG. l; and

FIG. 3 is an enlarged detail view, in cross-section, of a portion of the structure shown in FIG. l.

Referring to the drawing, the field magnet 1 includes a cere plate 2, a pair of permanent magnetsectors 3, and a top plate 4, all held securely together by bolts 5. TheA core plate 2 and the top plate 4 are preferably composed of soft iron. lA central core member 6 and a core tip or inner pole piece 8 are bolted together and to the core pla-te 2 by a screw 9. The inner pole piece 8 extends through a round hole la provided in the center of the top plate to form an outer pole piece, the inner and outer pole pieces being spaced to form an annular magnetic gap. A centering ring lil of a non-magnetic material, such as brass or aluminum, is aiiixed to the top plate and serves to center the core tip 3 within the hold 4a in top plate 4.

Positioned over `the core tip S, covering the upper face of this inner pole piece, and extending into the magnetic gap between the core 4tip and the top plate is an elastomeric centering body il. Embedded within the centering body is a voice coil l2 and a portion `of a voice coil bobbin d3. The bobbin and voice coil are maintained concentric with the magnetic gap by the centering body. A conical diaphragm it is affixed at its throat to the exposed end of the voice coil bobbin 13.

The centering body ll may be formed by any of several different methods. It may be formed by applying an elastomer-base adhesive primer to the surfaces of the pole pieces and the voice coil assembly, inserting the voice coil lassembly within the magnetic gap, filling the space between the voice coil assembly and the pole pieces with RTV Silastic elastomer, and then allowing the elastomer to set while the proper spacing of the voice coil assembly is maintained.

A preferred method is to prepare the voice coil assembly by mounting the voice coil on the bobbin and aiiixing it thereto by means of an epoxy resin. The diaphragm i4 may also be cemented to the bobbin 13 at this time by means of an epoxy resin. The sub-assembly comprising the bobbin, voice coil and diaphragm is then placed in a mold xture which maintains the voice coil assembly centered within the mold cavity. The liquid elastomer is then poured into the mold through the inside of the tube formed by the bobbin. The elastomer flows under the voice coil and bobbin and rises into a cavity between the mold and the outside of the voice coil and part of the bobbin, completely covering and embedding the voice coil and the lower portion of the bobbin. It is advantageous to contour the mold cavity in such a manner that the introduction of elastomer over and above that required to embed the voice coil forms a web integral with the inner portion of the elastomeric body in the form of a partition across the entire inner diameter of the bobbin. It is additionally advantageous to pour a surplus of elastomer into the bobbin cavity to make the web thick enough so that it extends to and seals itself to the inner surface of the throat of the diaphragm, forming a water-tight seal. The sub-assembly is inserted into the magnetic gap by forcing the centering body axially into the magnetic gap until the web 11a comes to rest against the core tip. Conveniently, the centering body is dimensioned to completely till the magnetic gap. If desired, an adhesive may be applied to cement the centering body to the pole pieces.

The diaphragm supporting frame is comprised of a plurality of spacing posts l5 aflixed at one end to the upper plate 4 by any suitable means such as silver soldering. The diaphragm rim 14a is clamped in position by means of clamping rings 16 and screws 17, gaskets 18 being interposed, if desired. A protecting cover 19, having a skirt 19a depending therefrom, is also held in place by the screws 17 and offers physical protection for the diaphragm 14. A plurality of apertures 20 are provided in the cover, both in its face and in the skirt portion to permit proper operation of the speaker' and also to assure equalization of pressure at both surfaces of the diaphragm.

Insulated leads 21 are brought out from the voice coil and are connected Vto a terminal strip 27 to which external connections may be made.

The disposition of the sector magnets 3 is shown in FIG. 2. This structure is utilized here in preference to a ring magnet, in order to allow better access to, and more space for the terminal strip, and, when desired, to permit an activating coil to be inserted about the central magnet for the purpose of magnetizing it, and for the subsequent removal of the coil. If desired, however, where other means are provided for bringing out the voice coil leads, a continuous ring magnet may be used.

The elastomeric centering body 11 may be composed of any suitable elastomeric material. Among such materials are natural rubber, artificial rubbers such as butadiene polymers and copolymers, acrylonitrile polymers, silicone rubbers, or other elastomers known in the art. The type of elastomer will be dictated by the intended use of the loudspeaker. For example, where low stiffness of the moving system is desired, an elastomer which is more resilient may be used. On the other hand, where stiff diaphragm characteristics are desired, an elastomer having less resiliency may be used. To decrease stiffness even further, a foamed elastomer may be used and may be foamed in place within the gap around the voice coil. Alternatively, the centering body may be preformed and the voice coil, centering body and voice coil bobbin, and diaphragm may be prefabricated as a unit. For uses in situations where the reproducer will be submerged under water at low temperatures for extended periods, elastomers having good low temperature elastic properties may advantageously be used. A preferred material is a silicone rubber marketed under the trademark RTV Silastic.

The core plate 2 and the top plate 4 should be composed of soft iron. The sector magnets 3 and the central core element 6 should preferably be made of a material having strong permanent magnetic properties such as Alnico V. Other materials such as ceramic magnetic materials may be used. The core tip 8 may be composed either of soft iron or of a permanent magnetic material. lf desired, soft iron may be used for either the sectors 3 or the central magnet 7, as a sutiiciently strong magnetic field may be produced by the remaining permanent magnet.

For normal uses, the speaker cone or diaphragm 14 may be made of any common material used in the art. However, where the cone must withstand the effects of sea Water and shocks such as that produced by the detonation of depth charges, care must be used in the choice of suiciently durable material. A suitable cone designed to withstand these forces may be produced by molding the cone from a plurality of layers of a nely woven fabric impregnated with a phenolic resin, which is subsequently molded and cured under pressure and heat.

The present loudspeaker has proven itself to be remarkably suitable for use where it is to be subjected to the ravages of extended submersion in salt water. It has been tested under the conditions encountered by submarine service and has continued to function even after continued and repeated submersion in salt water, even at very low temperatures. It has also withstood tests in which it was subjected to the pressures of explosive blasts. ts ability to withstand such forces is due to a large extent to the fact that the throat of the cone is firmly, albeit resiliently, supported by the core tip 8. The elastomeric centering body serves `as a cushion to receive and limit shocks. Web 11a of this centering body serves both to contribute to the sealing of the voice coil region of the speaker from water and other deleterious external agents,

Y and to prevent more than normal movement of the voice coil assemblyl inwardly in consequence, for example, of blast pressures exerted upon exposed external parts of the loudspeaker.

, As a study of the drawing will clearly show, almost all surfaces of the loudspeaker, including front and back surfaces of the relatively fragile diaphragm, are openly exposed to ambient atmosphere or other iiuid so that a shock pressure Wave substantially neutralizes itself by exerting Iits forces against opposite surfaces of the speaker parts. Pressures exerted against web 11a of the voice coil centering body have no effect since it is backed up by the end of core tip it.

Despite its ruggedness, the present reproducer is fully operative to provide a Satisfactory level of intelligible sound communication over an extended area.

We'claim:

l. A blast-proof water-proof loudspeaker comprising a iield magnet defining a magnetic gap and a diaphragmsupporting frame mounted on said magnet, an elastomeric voice coil centering body positioned Within and substantially filling said magnetic gap, said centering body supported by and having a portion thereof maintained in fixed relationship with said field magnet, a voice coil bobbin, a voice coil mounted on said bobbin centrally positioned within said magnetic gap and substantially embedded and Sealed within said elastomeric centering body, a conical diaphragm affixed at the throat thereof to said bobbin and clamped at its periphery to said frame, both the front and back surfaces of said diaphragm being exposed to ambient atmosphere, and a web integral with said centering body defining a transverse partition adapted to seal said bobbin against the passage'of fluid therethrough.

2. A voice coil diaphragm sub-assembly adapted for insertion Ainto the magnetic gap of a held magnet to cooperate therewith to form a blast-proof water-proof loudspeaker, said sub-assembly comprising an annular elastomeric voice coil centering body, a cylindrical bobbin, a conical diaphragm aiiixed at the throat thereof to said bobbin, a voice coil mounted on said bobbin and cornpletely embedded within said centering body, and a web integral with said centering body defining a transverse partition adapted to seal said bobbin against the passage of fluid therethrough.

References Cited in the tile of this patent UNITED STATES PATENTS 2,404,784 Bostwick July 30, 1946 2,648,837 Mounce Aug. 11, 1953 2,755,343* Levy July 17, 1956 FOREIGN PATENTS 899,674 Germany Dec. 14, 1953 1,126,904 France Aug. 6, 1956 '1,136,866 France Jan. 7, 1957 

1. A BLAST-PROOF WATER-PROOF LOUDSPEAKER COMPRISING A FIELD MAGNET DEFINING A MAGNETIC GAP AND A DIAPHRAGMSUPPORTING FRAME MOUNTED ON SAID MAGNET, AN ELASTOMETRIC VOICE COIL CENTERING BODY POSITIONED WITHIN AND SUBSTANTIALLY FILLING SAID MAGNETIC GAP, SAID CENTERING BODY SUPPORTED BY AND HAVING A PORTION THEREOF MAINTAINED IN FIXED RELATIONSHIP WITH SAID FIELD MAGNET, A VOICE COIL BOBBIN, A VOICE COIL MOUNTED ON SAID BOBBIN CENTRALLY POSITIONED WITHIN SAID MAGNETIC GAP AND SUBSTANTIALLY EMBEDDED AND SEALED WITHIN SAID ELASTOMERIC CENTERING BODY, A CONICAL DIAPHRAGM AFFIXED AT THE THROAT THEREOF TO SAID BOTTOM AND CLAMPED AT ITS PERIPHERY TO SAID FRAME, BOTH THE FRONT AND BACK SURFACES OF SAID DIAPHRAGM BEING EXPOSED TO AMBIENT ATMOSPHERE, AND A WEB INTERGRAL WITH SAID CENTERING BODY DEFINING A TRANSVERSE PARTITION ADAPTED TO SEAL SAID BOBBIN AGAINST THE PASSAGE OF FLUID THERETHROUGH. 